So I'm making an urban fantasy hidden world type of series. My #1 main character- Sarah- is (unsurprisingly) the main entry point into understanding the hidden supernatural world in terms of audience perspective. We see bits and pieces from other major characters who are already aware before she is, but it's more through her journey than anyone else's that we enter the hidden world. This journey is mainly about the character's own condition- psychologically and...otherwise. She has from the beginning of the story, a history of mental illness that affects her mood, producing volatile behaviour (some form of bipolar, I think). But, at this point in her life, she's managed to deal with it fairly well. However, as the story progresses, thinks rapidly begin to get worse for her, not only in intensity, but new symptoms. As it happens, her mental illness is itself a symptom of something bigger- a supernatural ancestry, that has been influencing her mind even while most of the supernatural traits have remained dormant. Her supernatural side has different inclinations and it's conflict with her human side has produced instability, in the form of her mental illness. While Sarah's mental illness isn't normal exactly, so not everything will be based in reality, it's not as if everyone thinks she's seeing things "but everything she sees is real!". She is experiencing, at the very least, something very much like real mental illness, if not simply mental illness with added supernatural factors. So my questions are: what is the correct balance between accurate depictions of mental illness and depictions of supernatural influence for such a story? And what are the general rules for depicting mental illness with other goals affecting the depiction in mind- what should I definitely include or avoid? I'm no expert in psychology nor someone with a whole load of personal experience so tips from people in either position particularly would be appreciated.